Elon Musk says prototypes are easy, production is hell. And when it comes to the long-awaited Cybertruck, Tesla's hell is its pioneering 4680 battery.

Tesla delivered the first of its futuristic stainless steel-plated electric pickups last month and CEO Musk said in October that it would probably hit an annual production rate of a quarter of a million vehicles at some point during 2025.

But Tesla is still a long way off that kind of production pace, and one of the main bottlenecks is the speed it can make the 4680 batteries used in the Cybertruck with its new dry-coating technology, nine people familiar with the matter said